docs: def lookup_value(self, api_name, key):
          """Add the value of an API call to the cache.
  
          Args:
              api_name: a string name of the API. Keys and values are segmented by api_name.
              key: a string key for the specific call.
          """
          if api_name in self._cache:
              return self._cache[api_name].get(key, None)
          return None